The proposed SMPTE-240M standard for high definition digital video specifies that each frame of an SMPTE-240M video signal consists of 2200.times.1125 pixels, and that the frame rate is 30 video frames per second. There are 2200 pixels per line, including 1920 active video pixels and 280 pixels which comprise a horizontal blanking interval. Of the 1125 lines allocated to each frame, 1035 lines represent an even field and an odd field, and ninety lines comprise a vertical blanking interval. The vertical blanking intervals contain synchronization information.
Optionally, four of the ninety "vertical blanking interval" lines contain information specific to a particular frame. Also optionally, a total of 1080 lines (including forty-five of the "vertical blanking interval" lines) can be employed for creating square pixels.
It would be desirable to store 1920.times.1080=2,073,600 pixels defining a high definition video frame in a standard "two megabyte" memory (a memory capable of storing 2.sup.21 =2,097,152 pixels). It would also be desirable to store such a set of 1920.times.1080 pixels, in a standard two megabyte memory, in a manner so that the pixels can be conveniently read out from memory in either an "interlaced" format or a "progressive" format.
To transmit a video signal in an "interlaced" format (or read the signal in interlaced format from memory), the odd field of each frame is transmitted (or read) before the even field of the frame. In other words, all the odd-numbered active video lines of the frame are transmitted (or read) before any of the even-numbered active video lines are transmitted (or read). When a video signal in such interlaced format is displayed on a video monitor, all of the odd lines appear on the monitor before any of the even lines appears on the monitor.
To transmit (or read) a video signal in a "progressive" format, the active video lines of a frame are transmitted (read) in consecutive order (line "1," followed by line "2," followed by line "3," and so on). When a progressive-format signal is displayed on a video monitor, the lines appear on the screen in this same consecutive order (with an odd line appearing immediately before each even line).
Until the present invention, it was not known how to write data representing a high definition video frame into a memory, in a manner so that the data could be efficiently read from the memory in a selected format (either an interlaced format or a progressive format).